1. Field of the Invention
The present invention relates to a magnetic tape unit provided with a magnetic read/write head which is arranged to simultaneously access a plurality of tracks on a magnetic tape for data-writing and data-reading.
2. Description of the Related Art
Magnetic tape units have been widely used as e.g. external storage apparatus for a computer system. To write and read data from the tracks (user data tracks) provided on a magnetic tape, use is made of a read/write head arranged in facing relation to the tape. Typically, such a magnetic head is provided with a plurality of channels the number of which is equal to the number of the tracks on the tape. In this equal-number arrangement, no mechanism is provided for adjustably moving the magnetic head in the widthwise direction of the tape.
One way to increase the recording density of a magnetic tape is to increase the user data tracks. Accordingly, the channels of the magnetic head is also increased. There is a limit, however, to the number of the head channels on grounds of performance and cost. Thus, in an instance where the magnetic tape is provided with a greater number of tracks than the head channels, it is necessary to move the magnetic head in the widthwise direction for causing the head to access any selected tracks on the tape. For controlling such widthwise movement of the head, servo control tracks are additionally provided on the tape. An example of thus arranged magnetic tape unit is disclosed in JP-A-7(1995)-57229.
In the conventional magnetic tape unit, however, there may be a problem of deterioration of the SNR (signal-to-noise ratio) when the magnetic tape and the magnetic head fail to be held in proper facing relation to each other. With an unduly reduced SNR, an error may occur in reading or writing data.
Further, in the conventional unit, the magnetic head is brought to a selected point of the magnetic tape (in its longitudinal direction) in a xe2x80x9crelativexe2x80x9d controlling manner. Specifically, the conventional unit is provided with reel motors for moving the magnetic tape forward or backward past the magnetic head. Each reel motor is associated with a sensor for counting the number of revolutions of the relevant motor. Based on the resulting count number and some other information, the longitudinal positioning of the magnetic head relative to the tape is performed. This means that the longitudinal position of the tape is not directly detected, but only indirectly (or relatively) through the operation of the reel motors. In this manner, however, a detection error will occur e.g. when the magnetic tape is slipped on the tape guides driven by the reel motors.
Still further, in the conventional unit, the running speed of the magnetic tape is calculated based on the revolution number of the reel motors measured within a certain period of time. In this manner again, only the xe2x80x9crelativexe2x80x9d tape speed can be known through the operation of the motor, while the actual tape speed may fail to be detected.
The present invention has been proposed under the above-described circumstances. It is, therefore, an object of the present invention to provide a magnetic tape unit capable of performing data-reading and data-writing operations with great accuracy. To this end, the following technical measures are taken.
According to a first aspect of the present invention, there is provided a magnetic tape unit including a magnetic tape, a magnetic head, a relative position determiner and a position compensator.
The magnetic tape is provided with a plurality of tracks including at least first and second servo control tracks. Each of the servo control tracks is provided with identical pieces of data which are spaced from each other in the longitudinal direction of the tape, wherein the pieces of data on the first servo control track are aligned with the pieces of data on the second servo control track in a widthwise direction of the tape.
The magnetic head is arranged to simultaneously access a plurality of tracks on the tape for data-writing and data-reading.
The relative position determiner determines the relative positional relation between the magnetic head and the magnetic tape based on signals read out from the servo control tracks.
The position compensator keeps the magnetic head and the magnetic tape in proper positional relation by adjusting the relative positional relation between the head and the tape based on the determination of the relative position determiner.
With such an arrangement, the detected skew of the magnetic tape relative to the magnetic head can be compensated based on the difference in phase of read-out signals obtained from the servo control tracks. Further, the facing relation between the magnetic head and tape can be adjusted based on the difference in level of the read-out signals from the servo control tracks.
According to a second aspect of the present invention, there is provided a magnetic tape unit which includes a magnetic tape, a magnetic head and a running condition determiner.
The magnetic tape is provided with a plurality of tracks including at least one servo control track provided with pieces of data spaced from each other in a longitudinal direction of the tape.
The magnetic head is arranged to simultaneously access a plurality of tracks on the tape for data-writing and data-reading.
The running condition determiner determines the running condition of the tape based on a signal read out from the servo control track.
The running condition of the tape may be a running position of the tape relative to the magnetic head. Here, the running position of the tape means the longitudinal position of the tape which the magnetic head is currently facing.
Another example of the running condition of the tape may be a running speed of the tape relative to the magnetic head. Here, the running speed of the tape refers to the current speed of the tape at which the magnetic tape is moved relative to the magnetic head.
With the above arrangement provided by the second aspect of the present invention, the running position or speed of the magnetic tape can be correctly determined by counting on the read-out signals from the servo control tracks, even if slippage occurs between the magnetic head and a tape feeding mechanism.
According to the second aspect of the present invention, the magnetic tape may be provided with two or more servo control tracks. The respective servo control tracks may be provided with pieces of data at non-aligned intervals. In this case, the running position of the magnetic tape can be more accurately determined by counting the pulses of signals obtained from the servo control tracks.
Further, a servo control track may be provided with pieces of data spaced from each other at partially non-equal intervals. In this case, it is possible to reduce the scale of a counting circuit for performing counting on a read-out signal obtained from the servo control track.
According to a third aspect of the present invention, there is provided a magnetic tape unit which includes a magnetic tape, a magnetic head and a position determiner.
The magnetic tape is provided with a plurality of tracks including at least one servo control track. This servo control track is provided with pieces of absolute position data which are spaced from each other in the longitudinal direction of the tape.
The magnetic head is arranged to simultaneously access a plurality of tracks on the tape for data-writing and data-reading.
The position determiner determines a running position of the tape based on information read out from the servo control track.
With the use of absolute position data, it is possible to eliminate the error in determining the running position of the tape which would otherwise occur due to the slippage of the tape. Here, the xe2x80x9cabsolute position dataxe2x80x9d refers to data which by itself identifies a longitudinal position of the magnetic tape.
According to a fourth aspect of the present invention, there is provided a magnetic tape unit which includes a magnetic tape, a magnetic head, a facing relation determiner and a facing relation compensator.
The magnetic tape is provided with a plurality of tracks including at least one servo control track provided with pieces of data.
The magnetic head is arranged to simultaneously access a plurality of tracks on the tape for data-writing and data-reading.
The facing relation determiner determines, based on a level of a signal read out from the servo control track, whether or not the magnetic head is held in proper facing relation to the magnetic tape.
The facing relation compensator adjusts the facing relation between the head and the tape based on the determination of the facing relation determiner.
With such an arrangement, for instance, the magnetic head may be slightly moved toward the magnetic tape, or vice versa, when the level of the read-out signal from the servo control track is smaller than the predetermined reference value. In this manner, the distance between the magnetic head and the magnetic tape can be optimized.
According to a fifth aspect of the present invention, there is provided a magnetic tape unit which includes a magnetic tape, a magnetic head, a non-magnetic portion detector and a running condition determiner.
The magnetic tape is provided with a plurality of tracks including at least one servo control track. This servo control track is provided with non-magnetic portions spaced from each other in a longitudinal direction of the tape.
The magnetic head is arranged to simultaneously access a plurality of tracks on the tape for data-writing and data-reading.
The non-magnetic portion detector detects the non-magnetic portions based on a signal read out from the servo control track.
The running condition determiner determines a running condition of the magnetic tape based on the detection of the non-magnetic portion detector.